Preheat oven to 375. Grease regular sized muffin tin (see Notes below for mini muffins).
In a large bowl, whisk together the flour, garlic powder and baking powder. Stir in the milk and egg, then add in the mozzarella, pepperoni, and green onions (if using) and mix together. Let stand for 10 minutes.
Briefly stir the batter and divide among the muffin cups, filling each cup about 1/3-1/2 full. Top with sliced olives, if using. Bake until puffed and golden, 25-30 minutes.
Meanwhile, warm the pizza sauce until warmed through.
Gently slide a knife around edges to loosen muffins. Muffins are puffy and fragile. Serve hot.
Serve the pizza puffs with the pizza sauce and ranch dressing for dipping.